ae series heat resistant compression casting magnesium alloy containing cerium and lanthanum

ABSTRACT

This invention relates to an AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum and the composition ingredients and the weight percentage thereof are as follows: Al: 3%˜5%, Ce: 0.4%˜2.6%, La: 0.4%˜2.6%, Mn: 0.2%˜0.6%, and the remainder is magnesium. The raw material of cerium lanthanum mixture of rare earth used is the residual, cheap and overstocked cerium lanthanum mixture of rare earth obtained from common cerium rich mixture of rare earth after the Nd, Rr with high value and good market have been separated. The mechanical performance of this invention at room temperature and high temperature excels that of AE 44 and AZ 91 alloys, and the minimum creep rate of 1.82×10-9 S-1 and the creep percentage elongation in 100 h of 0.17% at the condition of 200° C. and 70 MPa excel these of AE 44 alloy.

TECHNICAL FIELD

The present invention relates to a magnesium alloy material, and more particularly, to an AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum.

BACKGROUND ART

In recent years, due to the pressure of environment protection and the enhancement of energy saving consciousness, the light compression casting magnesium alloys mainly in Mg—Al based alloys have found extended application in automobiles. However, as compared with aluminum alloys, the application of magnesium alloys still drops behind greatly and one of the reasons thereof is being short of sufficient high temperature property. At present, the long-term service temperatures of the AZ, AM series compression casting magnesium alloys used widely can not excess 120° C., which makes them can not be used in manufacturing automobile driving assemblies that requires high creep resistant performance at high temperature, therefore the further application of magnesium alloys is blocked greatly. On the basis of that, the rare earth and alkali earth elements have been introduced into Mg-Al based alloys to develop a magnesium alloy with a creep resistant performance at high temperature, however, there are still some problems existing in this kind of heat resistant magnesium alloys developed recently. The main disadvantages existing in Mg—Al—Ca (AX) and Mg—Al—Sr (AJ) alloys are that thermal cracking occurs easily and the inferior plastic property of the alloys, and the like. The rare earths used in Mg—Al—Re alloys (herein, referred to as “AE series alloys”) developed are cerium rich mixture of rare earths (including La, Ce, Pr and Nd), however, the prices of Pr, Nd keep rising at present which makes the costs of this kind of AE series alloys increased. Additionally, the mechanical performances of the heat resistance magnesium alloys developed presently still need to be improved.

As the alloying (microalloying) elements for improving the heat resistant performance of the traditional magnesium alloys and developing new heat resistant magnesium alloys, rare earths have been recognized by the scientific research departments and manufacturers in China and abroad, and the rare earths used include single pure rare earth (such as Nd, Y, Gd) and mixture of rare earths. At present, the mixture of rare earths used mostly are: cerium rich mixture of rare earths with La, Ce, Pr, Nd as the main ingredients thereof, yttrium rich mixture of rare earths with Y, Ho, Er, Gd as the main ingredients thereof, praseodymium neodymium mixture with Pr and Nd as the main ingredients thereof. However, at present what overstocked abundantly is another cerium lanthanum mixture which is cheaper than the rare earths described above. Therefore, developing an application market of the cerium lanthanum mixture is pressing and significant for the complex utilization and equilibrium development of the rare earths.

Due to the specific chemical activity of cerium and lanthanum, after being added into magnesium alloys, both of them can produce the following four effects: purification, activation, fining and alloying/microalloying effects. As compared with other rare earth elements, lanthanum has better impurity removing (remove the hydrogen and oxides inclusions) and purification effects on alloys. Comparing with lanthanum, cerium has a higher solid dissolving degree and a better effect of fining the alloy texture in magnesium alloys. It has been recognized widely by researchers that lanthanum and cerium can elevate the allround performance of magnesium alloys. By utilizing cerium lanthanum rare earths in combination, exerting their respective advantages and developing new rare earths magnesium alloys with high performance, it can help to solve the problem of overstocking abundantly rare earth resource of cerium lanthanum mixture, to alleviate the contradiction of the resource between production and demand and to solve the problem of imbalance between production and distribution.

DISCLOSURE OF THE INVENTION

For overcoming the shortcomings of the present compression casting magnesium alloys, this invention provides an AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum. This alloy has a low cost, a good heat resistant performance and a long-term service temperature up to 200° C.

The ingredients and their mass percentage proportions of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum are as follows: Al: 3%˜5%, Ce: 0.4%˜2.6%, La: 0.4%˜2.6%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium.

According to some embodiments, the preparation method of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum of this invention is as follows:

Firstly, weighting according to the proportions, pure magnesium, aluminum, aluminum manganese intermediate alloy and manganese-cerium lanthanum intermediate alloy are pre-heated to 200° C., then pure magnesium, aluminum, aluminum manganese intermediate alloy are put into a crucible preheated to 300° C. and a protective gas with a SF₆/CO₂ volume ratio of 1:100 is introduced. After the materials added have been molten completely and when the temperature of the melt reaches 720° C.˜740° C., manganese-cerium lanthanum intermediate alloy is added and the introduction of the protective gas is continued. After the manganese-cerium lanthanum intermediate alloy added has been molten completely and when the temperature rises back to 720˜740° C., stirring for 5˜10 min, then refining for 5˜10 min with blowing argon. After the refining, settling for 28˜32 min and the melt is cooled to 680° C.˜700° C. A compression casting is performed on a cold chamber compression casting machine under a mould clamping force of 500 KN and an AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum is obtained. Said cerium and lanthanum as raw material used in the manganese-cerium lanthanum intermediate alloy can take the form of residual and cheap cerium lanthanum mixture obtained by separating Nd and Rr with high value from the common cerium rich mixture of rare earths.

The features and beneficial effects of this invention are as follows:

-   -   1) Aluminum is a main alloy element in an alloy, and an adequate         amount of aluminum can provide an alloy with balanced strength,         plastic property and casting processing performance, and makes         this invention be fit for mass production. 2) Cerium lanthanum         rare earth mixture is an element of this invention for         increasing the strength and the heat resistant property of an         alloy in a strengthen mechanism as follows: on the one hand, as         Al₁₁RE₃ and Al₂RE are formed by the combination of rare earth         and aluminum in the alloy, Mg₁₇Al₁₂ phase with poor thermal         stability is reduced or restrained which helps to increase the         high temperature performance of the alloy; on the other hand,         the Al-RE compounds of Al₁₁RE₃ and the like produced have very         high melting point (e.g., the melting point of Al₁₁RE₃ can be up         to 1200° C.). These compounds disperse in grain boundary and         show very high thermal stability which can nail the grain         boundary effectively to block the slippage of the grain boundary         and restrain the climb of dislocation in crystal. Additionally,         during smelting, cerium lanthanum rare earth mixture can remove         the impurities in manganese alloy melt to achieve the effects of         degas refining and purifying the melt. Cerium lanthanum rare         earth mixture is a surface-active element of manganese alloy.         During the smelting of an alloy, the rare earths gather on the         surface of the alloy liquid and a multiple composite dense oxide         layer of MgO, RE₂O₃ and A1 ₂O₃ is formed, which alleviates the         oxidation phenomenon, elevates the initial burning temperature         and favors the melt casting of the alloy. During the freezing of         the alloy liquid, the rare earths gather at the advancing front         of the solid and liquid to increase the supercoolling degree of         the ingredients and help to fine the alloy texture. Therefore,         cerium lanthanum mixture of rare earth benefits the improvement         of the allround performance of an alloy. 3) The main effect of         manganese is to increase the corrosion resistant performance of         an alloy, and manganese can form a compound with iron or other         heavy metal elements in magnesium alloy so as to remove them as         a slag. As a result, the harmful effect of iron or other heavy         metal elements on the corrosion resistance of the magnesium         alloy can be eliminated. 4) The cerium lanthanum rare earth         mixture is the residual and cheap cerium lanthanum rare earth         mixture obtained by separating Nd, Rr with high value from         common cerium rich mixture of rare earth. From 1990s up till         now, the experts on rare earth in China and abroad have paid         great attention to the problem of imbalance on the application         of rare earths. At present, a difficult problem affecting the         complex utilization and equilibrium development of the rare         earths is the abundant overstock of cerium lanthanum rare earth         mixture. Only in China, almost 12,0000 tons of cerium lanthanum         rare earth with a value of one hundred million dollars is         produced each year, however, this cerium lanthanum rare earth         mixture is always kept overstocked and has not been widely         utilized, which becomes a bottleneck for the complex utilization         and equilibrium development of the rare earths. The reasons that         this invention develops an AE series heat resistant compression         casting magnesium alloy containing cerium and lanthanum by         utilizing cheap cerium lanthanum mixture of rare earth lie         in: 1. utilizing the cerium lanthanum rare earth overstocked in         magnesium alloy which has been referred to as “a green light         engineering material of the 21^(th) century”, which can         alleviate the problem of imbalance between production and         distribution for rare earth source and can benefit the         harmonious development of the utilization of many rare earth         elements; 2. reducing the costs of this kind of alloys and         ensuring the continuable development of these alloys by the         abundant cerium lanthanum rare earth resource, which can         increase the competition of magnesium alloys and accelerate the         development of rare earth magnesium alloys nicely and quickly.

DESCRIPTION OF THE DRAWING

FIG. 1 shows the scanning electron microscope and transmission electron microscopy microtexture scheme for AlCeLa 4, 2.4, 1.6 alloy in Example 4. It can be seen that the main reason that the alloy has good mechanical performance lies in a fine grain strengthen of the alloy produced by fined alloy grains and a dispersion strengthen (mainly grain boundary strengthen) of the alloy produced by the abundant fine high melting Al-RE at the grain boundary.

FIG. 2 shows curve 1 and curve 2 as the creep curves of AlCeLa 4, 2.4, 1.6 alloy in Example 4 of this invention and AE 44 alloy under the condition of 200° C. and 70 MPa, respectively.

BEST MODE OF CARRYING OUT THE INVENTION EXAMPLE 1 AlCeLa 3, 0.6, 0.4 Alloy

The mass percentage proportions of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum are as follows: Al: 3%, Ce: 0.6%, La: 0.4%, Mn: 0.2%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium. The performance of the alloy is shown in FIG. 1 and FIG. 2.

EXAMPLE 2 AlCeLa 5, 1.2, 0.8 Alloy

The mass percentage proportions of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum are as follows: Al: 5%, Ce: 1.2%, La: 0.8%, Mn: 0.4%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium. The performance of the alloy is shown in FIG. 1 and FIG. 2.

EXAMPLE 3 AlCeLa 4, 1.8, 1.2 Alloy

The mass percentage proportions of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum are as follows: Al: 4%, Ce: 1.8%, La: 1.2%, Mn: 0.4%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium. The performance of the alloy is shown in FIG. 1 and FIG. 2.

EXAMPLE 4 AlCeLa 4, 2.4, 1.6 Alloy

The mass percentage proportions of the AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum are as follows: Al: 4%, Ce: 2.4%, La: 1.6%, Mn: 0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium. The performance of the alloy is shown in FIG. 1, FIG. 2 and FIG. 3.

TABLE 1 The mechanical performances of Example 1, 2, 3 and 4 of this invention at room temperature Tensile Yield Percentage Alloy No. strength (MPa) strength (MPa) elongation (%) Example 1 228 130 15 Example 2 245 135 10 Example 3 257 148 13 Example 4 271 160 14 AE44 248 140 11 AZ91 222 145  3

TABLE 2 The mechanical performances at high temperature of Example 1, 2, 3 and 4 in this invention 150° C. 200° C. Tensile Yield Percentage Tensile Yield Percentage strength strength elongation strength strength elongation Alloy No. (MPa) (MPa) (%) (MPa) (MPa) (%) Example 1 134 94 26 105 80 23 Example 2 140 103 21 108 87 20 Example 3 145 111 24 112 96 21 Example 4 147 120 31 120 107 26 AE44 140 109 27 115 100 19 AZ91 150 105 13 99 84 15

TABLE 3 the creep resistant performance at high temperature of AlCeLa 4, 2.4, 1.6 alloy in Example 4 of this invention 200° C., 70 MPa Percentage Minimum Persistent elongation creep life over 100 hrs rate Alloy No. (hours) (%) (×10⁻⁹ s⁻¹) Example 4 >100 0.17 1.82 AE44 >100 0.18 3.42

Table 1 shows the mechanical performances of the alloys in Example 1, 2, 3 and 4 of this invention and AE 44, AZ 91 at room temperature.

Table 2 shows the mechanical performances at high temperature of Example 1, 2, 3 and 4 in this invention and AE 44, AZ 91.

Table 3 shows the creep resistant performance at high temperature of AlCeLa 4, 2.4, 1.6 alloy in Example 4 of this invention and AE 44.

AE 44 is a new high temperature creep resistant compression casting magnesium alloy developed by Hydro Magnesium Industry Company in Norway in 2005 and has been applied to produce automobile parts, such as the cradle for engine in automobile. AZ 91 is a magnesium alloy with a standard trademark and is also one of the magnesium alloys with the most use level in industry at present, however the service temperature thereof can not excess 120° C. The data of AE 44 and AZ 91 in FIG. 1, FIG. 2 and FIG. 3 are the data obtained by preparing the samples at the same condition and testing them at the same condition 

1. An AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum, characterized in that the composition ingredients and the weight percentage thereof are as follows: Al: 3%˜5%, Ce: 0.4%˜2.6%, La: 0.4%˜2.6%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium.
 2. The AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum according to claim 1, characterized in that the composition ingredients and the weight percentage thereof are as follows: Al: 3%˜4%, Ce: 0.4%˜0.6%, La: 0.4%˜0.6%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium.
 3. The AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum according to claim 1, characterized in that the composition ingredients and the weight percentage thereof are as follows: Al: 4%˜5%, Ce: 1.0%˜1.2%, La: 0.8%˜1.0%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium.
 4. The AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum according to claim 1, characterized in that the composition ingredients and the weight percentage thereof are as follows: Al: 4%˜5%, Ce: 1.8%˜2.0%, La: 1.0%˜1.2%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium.
 5. The AE series heat resistant compression casting magnesium alloy containing cerium and lanthanum according to claim 1, characterized in that the composition ingredients and the weight percentage thereof are as follows: Al: 4%˜5%, Ce: 2.4%˜2.6%, La: 1.4%˜1.6%, Mn: 0.2%˜0.6%, the total amount of impurity elements of Fe, Cu and Ni is less than 0.03%, and the remainder is magnesium. 